The present invention relates generally to industrial processing, and more particularly, to improved apparatus and methods for devulcanizing elastomers or similar cross-linked polymers.
It is readily acknowledged that there is substantial motivation to develop practical methods and apparatus for devulcanizing rubbers, other elastomers, and in some cases, resinous products generally, i.e., polymer products that may be characterized as "cross-linked" or having a three dimensional molecular network.
In particular, rubber is used in million-ton quantities every year in the manufacture of tires, structural products, auto parts and in other applications too numerous to mention. The motivation for recycling rubber products is multi-fold. In one aspect, it is desirable to recycle rubber simply as the way of reducing the amount of waste and potential pollution that results from being unable to reuse the rubber incorporated into vehicle tires and other products.
Another aspect of the same problem is the economic benefit that could be gained by utilizing some or all the components of rubber or other elastomers again and again. In this connection, a great number of products are made from metal, particularly aluminum, that has been used one or more times. Such recycled material is capable of being used repeatedly, whether or not the material being recycled and reused meets the standards of virgin material.
At the present time, in the elastomer field, there are a number of products made from what may be termed "specialty rubbers" and these products, while able to deliver outstanding performance in difficult applications, have historically been characterized by very high cost. Merely by way of example, there are many automotive products, such as seals, diaphragms, gaskets, O-rings, and the like that are called upon to provide service under severe conditions and survive difficult and hostile environments for greatly extended periods, all without failure in use.
However, in the process of resisting high and low temperatures, abrasive stress, chemically threatening solvents and the like, such products have increasingly come to made from exotic elastomers, including, by way of example, polymers that include fluorine or other halogens, nitrogens, and phosphorous. Because of the extreme expense of these materials, there is additional recycling motivation, namely, the potential for greatly decreasing the cost of raw materials used in replacement products. Again, while all materials reclaimed from such a process may not be suitable, at least without modification, for making products which are identical to their counterparts made with virgin stock, the potential for making useful products from reconstituted polymers is still very great. It has been demonstrated that such polymers, when devulcanized by a process such as that comprising the present invention, may be reconstituted by the use of cross-linking or vulcanizing agents and other suitable steps into regenerated or like elastomers having at least some properties that are substantially similar to those of the non-degraded, original elastomer. In particular, materials such as so-called "FKM"s or fluoroelastomers possess the potential ability to be recycled into useful products at significant cost savings.
The potential of recycling such products has eluded most workers for some time; however, one proposal process for devulcanizing existing elastomers has now been discovered, and has been described in general form and claimed in U.S. Pat. No. 5,258,413 issued Nov. 2, 1993. This process is one that basically involves confining particles of cured elastomer within a particular treatment zone, advancing them along a given axis through the zone under pressure, as by a feed auger, and then and there subjecting them to ultrasonic energy propagated along such axis. It is said that this can rupture the various bonds located where the reactive sites were on the monomer before vulcanization. Also, it is said that it is possible to rupture bonds in the linear or branched (but not cross-linked) polymers. These bonds include the carbon-carbon (C--C) bond, the carbon-sulfur (C--S) bond, and the carbon-oxygen (C--O) bonds known to exist in cured elastomers.
The methods described in the above '413 patent also call for positioning an ultrasonic horn as such that it substantially obstructs the outlet diameter of a die through which the material being processed passes under the force generated by an extruder. In the examples described, the horn end face has a diameter that is significantly larger, i. e., approximately twice the diameter, of the die. The axial spacing between the end face and the die is described as being less than 1 millimeter for a horn diameter of 12.7 millimeters. In this patent, the axial clearance is only about 4% of the horn diameter and less than 10% of the outlet die diameter.
A subsequent patent, U.S. Pat. No. 5,284,625 describes a similar apparatus, differing from that of the '413 patent in that it is said that the horn may be inside the area wherein the rubber is confined but still arranged coaxially with the die outlet. Another arrangement of the ultrasonic horns is described wherein two non-circular horn end faces are arranged in facing relationship to each other or with the faces parallel to the direction of elastomer movement. In such arrangement, however, there is no discussion of any particular type of cooperation between the horns, nor is there a discussion of energy confinement as opposed to attempts to input energy to the mass of material being treated.
The present invention is directed to confining and using energy that would otherwise be lost, and is also concerned with greatly increasing the rate of treatment or "throughput" able to be achieved.
Although it is now recognized that ultrasonic energy may be used in such devulcanization, it has also been determined that prior attempts, including those described in the above-referenced patents, have not been as effective as they might have been. Thus, in the past, the amount of energy actually used to rupture the bonds and devulcanize the elastomers in question has been very small in relation to the overall energy input required for the process. It is difficult to transmit the requisite energy in the ultrasonic wave frequency band unless conditions are ideal, because among other things, the rubber particles are non-uniform and they serve to absorb and/or dampen the incoming wave. In addition, the construction and arrangement of the apparatus used to transmit energy into the mass of rubber has not been fully effective to transmit the necessary energy to the rubber.
Accordingly, an effort has been made to increase the rate and level of energy transfer from the ultrasonic apparatus to what may generally be termed the treatment zone of an ultrasonic devulcanization apparatus. According to the invention, it has been discovered that if an ultrasonic horn is arranged in a particular way, or if two or more ultrasonic horns are arranged in one or more ganged, phased or otherwise cooperating arrays, greatly increased efficiency in the rate of energy transfer may be achieved, with the result that the total energy brought to bear on the devulcanizing process can be greatly increased relative to that available using prior methods. This can greatly speed up the devulcanizing process and make it more effective.
Another aspect of the invention is that, whether or not single or multiple horns are used, the remainder of the apparatus should be constructed so as to be reflective rather than absorptive of the energy transmitted to and through what may be termed the treatment zone.
According to the invention, one method of achieving this result in practice is to provide at least a pair or other phased array or gang of ultrasonic energy generators, and connect them by a triggering or energy source that includes a delay line providing a suitable time delay. According to this practice, by way of example, a pair of opposed ultrasonic generators are positioned in a spaced apart relation from each other, spanning a treatment zone in which devulcanizable rubber particles are confined under pressure. According to the invention, the opposed or otherwise functionally connected horns are able to resonate with each other, greatly improving the energy transfer to the being-treated mass.
Suitable adjustments are made in the delay circuit such that the effect of the rubber in absorbing, damping, and/or delaying propagation of the waves breaking down the bonds is largely or almost entirely overcome. By properly phasing the ultrasonic generators or horns, a reinforcing wave pattern can be created whereby the wave amplitude can be increased. Standing waves may thus be created and used effectively. As will appear, various arrangements of the ultrasonic generator components can be made to achieve this purpose.
Another manner of achieving this result is to arrange a second ultrasonic energy device in a particular arrangement relative to the energy transmitting ultrasonic device, with the second device being constructed, arranged, and "tuned" to as to cause the energy it receives from the first device to be reflected back into the treatment zone.
In still other arrangements, it is possible to provide portions of the treatment zone, usually the "back wall" of the treatment zone, i.e., the part facing the horn, with a construction and arrangement such that this wall reflects rather than absorbs the energy transmitted to it.
Another manner in which the invention is practiced is the construction and arrangement of wave generating and/or reflecting elements in such a way that both compression and shear wave components of the energy are taken advantage of; this is done by analysis and subsequent arrangement of parts so as to confine the maximum amount of energy to the treatment zone.
More specifically, another way in which the invention achieves its objects is to bring the rubber in the reaction chamber into resonance and to confine the resonant energy to the mass of rubber so as to achieve useful work, usually in the form of a shear wave energy component that is actually used to break the molecular bonds.
Still another aspect of the invention is to make an efficient arrangement which utilizes not only a directly powered ultrasonic horn, but also a passive or horn component of an ultrasonic assembly only, without using the ultrasonic wave generator, and providing stackable elements or the like for mass tuning of the second or passive ultrasonic horn and amplifier. The manner in which tuning is achieved is preferably mechanical and involves a variation of the mass and its position relative to the horn. This horn can also be adjustably positioned for tuning purposes, i.e., its energy-propagating surface will be a desired distance, related to the wavelength of the energy, from the opposed horn.
There being significant room for improvement in the field of elastomer devulcanization, therefore it is an object of the present invention to provide an improved apparatus and method for devulcanizing elastomers.
Another object of one apparatus of the invention is to provide an improved apparatus for devulcanizing elastomers, with such apparatus including a treatment zone wherein particles of cured elastomer may be confined under pressure, with such zone having at least one ultrasonic generator disposed on each side thereof, with such generators being linked to each other by a triggering arrangement permitting control of the vibrating energy generated by each generator.
Yet another object of the invention is acceleration of the process and increase of the yield by causing the polymer being treated to flow perpendicular to the ultrasound wave front or direction of its propagation.
Another object of the apparatus of the invention is to provide a cross-linked polymer devulcanizing apparatus which includes one or more pairs of ultrasonic horns, the horns in each pair being linked to each other through a delay line mechanism, thereby permitting energy transfer of increased effectiveness by creating a greatly improved output wave form pattern and better energy transfer to the elastomer being treated.
A further object of the invention is arranging an array of individual ultrasonic generators about a treatment zone for devulcanizable elastomers, with the array being constructed and arranged so that the various individual horns or generators are actuated at a precise time in relation to actuation of the other generators in the system as a whole, to achieve a reinforcing or in-phase effect.
A still further object of the invention is to provide a method of rubber devulcanization which includes subjecting rubber particles to devulcanizing energy in the ultrasonic spectrum and which also includes arranging the individual generators in an array such that the generators will operate in phase with one another according to a predetermined plan, thus maximizing energy transfer to the mass to be treated.
Yet another object of the invention is to increase the reaction chamber volume by removing constraints on the way in which the wave is propagated. This improvement involves, but is not limited to, directing the flow of polymer perpendicular to the wave front.
Another object of one embodiment of the invention is to provide an apparatus for devulcanizing elastomers, which apparatus includes means for advancing particles of elastomer to be devulcanized to a treatment zone, and providing a phased array of ultrasonic generators spanning the treatment zone and constructed and arranged to furnish energy thereto in phase with one another as desired by the operator, with the apparatus further including a reduced temperature output area to reduce or eliminate possible degradation and/or revulcanization.
A further object of the invention is to provide a devulcanizing apparatus which uses a particular construction and arrangement of ultrasonic horns, one powered and the other tuned so as to reflect the energy supplied to the first horn into and through the reaction zone or chamber.
Yet another object of the invention is to provide an apparatus for ultrasonic devulcanization wherein wall thickness and other components of the apparatus are arranged so as to maximize energy confinement and minimize transmission of the compression wave energy supplied to the mass through the walls of the apparatus.
A still further object of the invention is to provide an arrangement whereby the largest possible proportion of compression wave energy is confined to the reaction zone and a portion of such energy is converted into shear wave energy causing molecular level devulcanization of rubber specimens.
Another object of the invention is to provide a rubber devulcanization apparatus wherein account is taken of the effective density of the confined rubber particles so as to "tune" the input energy to the wave transmission and energy absorption characteristics of the rubber mass under treatment.
Yet another object of the invention is to provide an apparatus capable of greatly increased speed of operation relative to known prior art rubber devulcanizers.
Still another object of the invention is to provide an improved apparatus using ultrasonic energy and capable of devulcanizing exotic or unusual elastomers, including fluorocarbon and other specialty elastomers at rates that are very favorable relative to known prior art methods of achieving rubber devulcanization.
The foregoing and other objects and advantages of the invention are achieved in practice by providing an apparatus wherein an elastomer devulcanization treatment zone is provided, and wherein the zone is defined at least in part by one or more ultrasonic generators arranged for improved energy transfer, such as providing two or more generators coupled by delay lines or other means so as to operate as a phased array in use of the apparatus, or as passive energy reflection, or by other structural changes to the treatment zone, so as to maximize energy concentration in the treatment zone.
The invention also achieves its objects by a method that includes synchronizing the output of plural ultrasonic generators producing devulcanizing energy in such a way and along such an axis as to maximize transfer of energy to the devulcanizable mass.
The manner in which the foregoing and other objects and advantages of the invention are achieved in practice will become more clearly apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.